By way of one example of light irradiation devices, an ultraviolet irradiation device has been used for general purposes, including fluorescence reaction observations in the field of medicine or biotechnology, disinfection, the adhesion of electronic components, and the curing of ultraviolet cure resin and ink (refer to Patent Literature 1, for example).
However, the light irradiation device may undergo changes in performance capabilities, such as a drop in optical power output, with the accumulation of irradiation time. Due to the accumulation of irradiation time, for example, the above-described curing may not complete successfully, causing incomplete curing, or the necessity of readjustment of curing conditions may arise. This has created demands for a light irradiation device capable of correcting changes in optical power output caused by the accumulation of irradiation time, for example.